Conventionally, magneto-optical recording media, which have been put into practical use as rewritable optical recording media, use a beam-condensed light beam released from a semiconductor laser so as to carry out recording and reproducing operations. However, the disadvantage with the magneto-optical recording medium is that in the case when the diameter of a recording bit serving as a recording magnetic domain or the interval of the recording bit is relatively smaller than the diameter of the light beam, its reproducing characteristic deteriorates.
This is caused by the fact that within the beam diameter of the light beam which has been beam-condensed on a target recording bit, adjacent recording bits of this bit tend to be included, with the result that individual recording bits can not be reproduced in a separated manner.
A construction which aims to overcome the above-mentioned disadvantage with the magneto-optical recording medium has been proposed in "Magnetically Induced Superresolution Using Interferential In-Plane Magnetization Readout Layer" (Jpn.J.Appl.Phys.Vol.35(1996) pp.5701-5704). In this construction, a reproducing layer, a non-magnetic intermediate layer and a recording layer are stacked in this order. This reproducing layer exhibits in-plane magnetization at room temperature, and comes to exhibit perpendicular magnetization as the temperature rises. Moreover, in this construction, the reproducing layer and the recording layer are magnetostatically coupled with each other with the non-magnetic intermediate layer interpolated in between so that a portion of the reproducing layer which is in a perpendicular magnetization state copies the magnetization of the recording layer. On the other hand, a portion thereof which is in an in-plane magnetization state masks the magnetization of the recording layer.
For this reason, information of recording bits in the recording layer at the portion in contact with the reproducing layer that is maintained in an in-plane magnetization state is not reproduced. Therefore, even if a target recording bit to be reproduced and a recording bit adjacent to this recording bit are included within a beam spot of the light beam, it is possible to reproduce the target recording bit individually in a separated manner.
Moreover, "Magnetic Super-Resolution Magneto-optical Disk using In-plane magnetization Mask Layer" (Japan Applied Magnetic Society Bulletin 21,1076-1081(1997)) has proposed a construction in which in order to achieve a higher reproducing resolution, the in-plane magnetization mask is strengthened by adding an in-plane magnetization mask layer having a low Curie temperature to a reproducing layer.
Furthermore, Japanese Patent Application No. 193140/1996 (Tokuganhei 8-193140), which was applied by the inventors of the present invention, has proposed another construction for further increasing the reproducing resolution of the magneto-optical recording medium, in which the Curie temperature of a reproducing layer is set lower than the Curie temperature of a recording layer so that the in-plane magnetization mask of the reproducing layer is used as a front mask while a portion of the reproducing layer having a temperature rise not less than the Curie temperature is used as a rear mask, thereby forming double masks.
However, the conventional magneto-optical recording media having the above-mentioned constructions have a problem in which, upon carrying out recording and reproducing operations by using an even smaller recording-bit diameter and even smaller recording bit intervals, a leakage magnetic flux, released from the recording layer, gradually grows with temperature rise, with the result that the mask effect of the reproducing layer becomes insufficient, thereby failing to provide a sufficient reproducing signal.